Certain natural fibers benefit digestive function, help prevent intestinal and colon cancer and act as fecal gastroenteral bulking agents. Generally, fibers are derived from grains, and are composed of polysaccharides with a range of structures.
Yeast cell walls are largely made up of the hydrophilic polysaccharide beta-glucan. The cell wall is primarily composed of a .beta.(1-3) linked glucose polymer with periodic .beta.(1-6) linked side chains. A similar polysaccharide can be found in grains, such as barley, which are common sources of dietary fiber.
It is known that a diet high in fiber is beneficial for a variety of reasons. Dietary fiber aids digestion because it provides an indigestible biomass which is carried through the alimentary canal causing undigested food to be pushed out before it. Fiber also clears out bacteria and insures the proper working of the peristaltic muscles. A diet high in fiber has been shown to reduce serum cholesterol and triglyceride levels, and has been linked to lower rates of intestinal and colon cancer. A high fiber diet has also been linked to the reduction of other problems commonly associated with poor digestion, such as ulcer formation, ileitis and colitis.
Dietary fiber is particularly important for persons on a liquid diet, such as, for example, a patient who receives nourishment through a feeding tube due to inadequate function of the gastrointestinal tract, with or without protein calorie malnutrition. A common side effect for those patients who do not receive any fiber supplement is chronic diarrhea due to lack of bulk. This condition may cause depletion of essential nutrients in the patient, dehydration and bowel irritation. Some dietary fibers can be used as a stool or fecal bulking agent to aid digestion and control chronic diarrhea. A fiber having a large water holding capacity is useful for this purpose, because these fibers absorb excess fluid in the colon resulting in increased fecal wet weight and stool number. Furthermore, some fibers are partially digested by bacteria in the large bowel, forming short chain fatty acids, which are preferred energy fuels for the small intestine and improve intestinal function.
Grain .beta.-glucans are commonly used as a source of fiber. Another source of .beta.-glucans is yeast cell walls; however, yeast .beta.-glucans have not been used as a dietary fiber supplement due to the fact that yeast cell wall glucans prepared by traditional methods, such as the method described by Manners et al., in Biochem. Journal, 135:19-30 (1973), are not pure, and generally contain materials such as protein, glycogen and chitin. Also, the water-holding capacity of .beta.-glucans prepared previously is low due to the presence of hydrophobic components such as protein and glycogen, and due to the lack of any three-dimensional cell wall micro-structure. Functionality and purity of a compound to be used for non-irritating, food-grade, fiber preparations are essential to ensure acceptable performance and qualitative properties, such as bland taste and white coloration.